It has been found advantageous in the chemical vapor deposition (CVD) art used in making integrated circuits to utilize high density plasmas to enhance chemical deposition, etching, or cleaning reactions in a substrate or substrate processing chamber. It is well known that high density plasma (i.e., 1.times.10.sup.11 to 2.times.10.sup.12 ions/cm.sup.3) wherein low energy bombardment of the processing surface (i.e., electron temperature T.sub.e .about.a few electron volts or eV) is attainable by use of inductively coupled plasma sources.
In the prior art inductive plasma sources, a helical antenna coil is typically wound about the exterior surface of a dielectric (quartz) dome or cylinder forming a portion of the vacuum processing chamber. An RF current (i.e., from about 100 KHz to about 100 MHZ) is passed through the antenna coil. When operated in a resonance mode with the applied RF power, an RF current, I.sub.RF, circulating in the antenna coil generates an axial RF magnetic field, B.sub.RF, within the processing chamber volume antenna coil. This magnetic field, B.sub.RF, induces a circulating RF electron current in the gas in the enclosed chamber to maintain a high energy plasma in the gas, once the plasma is lit (i.e., once the gas becomes partially ionized by electron collisions). The configuration formed may be considered an RF transformer with the antenna coil acting as the primary winding and the plasma, itself, acting as the secondary winding.
Such inductively coupled plasmas in the process chamber volume above a substrate tend to be non-uniform and annular in shape, having lower plasma density over the center portion of the PATENT processing surface. This "hollow center" effect can be alleviated by providing a top or cover antenna coil over the top portion of the dielectric cover of the processing chamber. Such top antenna coils have, in the prior art, been generally spirally wound and have not been used in conjunction with a gas inlet disposed through the top of the chamber. One example is found in U.S. Pat. No. 5,401,350, entitled "Coil Configuration for Improved Uniformity in Inductively Couple Plasma System". A centrally located gas inlet disposed through the top of the chamber has been found to enhance uniform deposition. One chamber which utilizes a center gas feed is the Ultima".TM. HDP-CVD chamber available from Applied Materials. This chamber utilizes a top and side coil to enable tuning of the power delivered to the chamber and enhance uniformity of the plasma.
It is an object of the present invention to provide an improved top antenna coil for a PECVD chamber which improves uniformity in a magnetic field generated above a substrate positioned in the chamber. It is a further object of the invention to provide an HDP-CVD chamber having improved uniformity across a plasma maintained above a substrate positioned in the chamber.